Titanium-base alloys



Patented May 13, 1952 UNITED STATES PATENT OFFICE TITANIUM-BAQFEA QOYSQ', Robert I. Jafiee, Horace R. and Daniel J. Maykuth, Columbus, Ohio, assignors, by mesne assignments, to Remington Arms ,Compan y, Inc., Bridgeport, Conn., al c oi'por'atiou of Dela} ware No Drawing. hppIicatiorr ltIaiich 2,1951, Serial-No. 213,689 1' T This invention relates to titanium-base alloys, and particularly to ternary alloys of titanium and aluminum with bismuth.

The use of titanium as a structural material is limited by its relatively low strength and high cost, and it becomes desirable to alloy titanium with such other metals as will increase the strength to acceptable levels and preferably at the same time effect some reduction in the total material cost. Aluminum is a metal well suited to the attainment of these objectives, being low in weight, relatively low cost, and having a material strengthening effect on titanium. However, the amount of aluminum alone that can be added to titanium is limited by its adverse effect on ductility. Binary alloys of titanium with more than about 5% of aluminum are too brittle for most structural uses; and such binary alloys containing less than about 5% of aluminum do not possess sufficient strength to be of general utility. A further strengthening is highly desirable.

The present invention comprises the discovery that the addition to titanium-aluminum alloys of 0.5% to about 5% of bismuth effects a marked improvement in the properties of titanium-aluminum-alloys of a given aluminum content, say 3.5% to 5%. The alloys show a rare combination of extraordinary strength with adequate ductility, notwithstanding the loss of some bismuth in melting.

The metal used as a base for the alloys of the present invention may contain the interstitial contaminants, carbon, oxygen and/or nitrogen, up to at least the total quantity to be found in good quality commercial titanium. Carbon, for example, has been found to be beneficial when present in amounts between 0.02% and 0.3%, the latter being about the maximum amount which is soluble in alpha titanium. An excess of carbon tends to form embrittling carbides. For a typical alloy, a carbon content of 0.1% to 0.2% is desirable, but the optimum amount varies with other factors. Nitrogen is a potent hardener of 'lClaims. (01.75 131) titaniumibuti tends tocause embrittlem'enti The effector the three contaminants being additive at ag'iven strength level, the quantity of each which can be tolerated depends to a considerable extent upon the quantity of the others. The limiting factor is usually ductility, and the requirement as to ductility varies with the intended use of the alloy. Further, increasing the amounts of the substitutional metallic alloying ingredients tends to decrease the tolerance for the interstitial components, particularly embrittling nitrogen. An alloy of high purity titanium with 5% aluminum will tolerate as much as 0.25% nitrogen, but the addition of one or two percent of another metal materially reduces nitrogen tolerance.

The alloys of this invention may be prepared by melt-casting in an atmosphere of argon, rolling at a suitable temperature, say 980 0., and annealing under conditions which will efiect recrystallization, but not substantial grain growth or re-solution of carbides. A typical but by no means universal annealing treatment comprises soaking at a temperature of about 850 C. for about 3 hours. The rate of cooling after annealing is not material, since in these alloys the titanium is all in the alpha phase except for minor amounts which may be combined as titanium carbide. The properties of selected alloys of titanium of requisite purity with aluminum and tin, as annealed for 3 hours at 850 0., unless otherwise noted, are as follows:

Typical properties of an alloy of substantially pure titanium with 0.25% carbon and 5% aluminum, as annealed for 3% hours at 850 0., are as follows:

Proportional Limit, p. s. i. 72,000 0.2% Oilset Yield Strength, p. s. i. 91,000 Ultimate Strength, p. s. i. 104,000 Elongation in 1 inch, percent 1'? The properties of selected alloys embodying the present invention, as annealed for 3 hours at 850 C., are as follows:

Intended Compo- Tensile Properties-p. s. i.

sition (Balance Titanium) P 0 27 E1 v. H. N. 0 Ultimate Bend A] Bi 0 Surface 23 3: 52 Strength 32 1 T as 0.5% oi bismuth substantially increases the strength of the titanium-5% aluminum alloy, with no loss of ductility. Increasing the bismuth addition to 2.5% tends to produce a furtherincrease in'strength, the loss in ductility being' slight. With a bismuth addition 'of 5%,' strength has increased materially and enough ductility remains to meet the requirements of a' wide-variety of uses. Due to relatively small differences between yield and ultimate strengths, the alloys find their greatest utility for uses: in which'the material is not stretched during fabrication.

What is claimed is: V

1. An alloy consisting essentially of from 3.5% to.5,% aluminum, from 0.5% to 5% bismuth, from 0.02% to 03% carbon, balance titanium.

2. An "alloy consisting essentially of about 5% 4 7 aluminum, from 0.5% to 5% bismuth, from 0.02% to 0.3% carbon, balance titanium.

' 3. An alloy consisting essentially of about 5% aluminum, from 0.5% to 5% bismuth, from 0.1%

i to 0.25 carbonf balance' titanium.

4. An alloy"consisting 'essentially of about 5% aluminum, from 0.5% to 2.5% bismuth, from 0.1% to 0.25% carbon, balance titanium.

'5. An-alloy consisting essentially of about 5% aluminum, 0.5% bismuth, from 0.1% to 0.25% earbon,-'balance titanium.

6. fAnalioy consisting essentially of about 5% aluminum, 1 .0% bismuth, from 0.1%

carbon, balance titanium.

7. An alloy consisting essentially of about 5% aluminum,-2;5% "bismuth, from 0.1% to 0.25% carb'on, balance titanium.

ROBERT I. JAFFEE. HORACE R. OGDEN. DANIEL J. MAYKUTH;

-No references cited. 

1. AN ALLOY CONSISTING ESSENTIALLY OF FROM 3.5% TO 5% ALUMINIUM, FROM 0.5% TO 5% BISMUTH, FROM 0.02% TO 0.3% CARBON, BALANCE TITANIUM. 